Power circuit for switching the number of poles on the rotor of synchronous machines by using rotative diodes

ABSTRACT

A circuit for changing the poles of a rotor of a synchronous machine having contact brushes in operative connection with first and second slip rings includes a switch for reversibly connecting the contact brushes to an electrical current source, reversible pole coils operatively connected to one of the slip rings and connected through a first diode to a circuit portion which is formed by irreversible pole coils, and by a second diode and a third diode, and which is operatively connected with the other of the slip rings, and a circuit branch including a fourth diode having a polarity reversed with respect to the polarities of the first, second and third diodes. One terminal of the fourth diode is connected between the reversible pole coils and the first diode and the other terminal of the fourth diode is connected between the irreversible pole coils and the second diode.

The present invention relates to a circuit for changing poles of a rotorof a synchronous machine.

In many branches of industry in which electrical synchronous machinesare utilized, it is necessary to change the poles of the rotors. This isparticularly important in power plants. When certain hydrauliccircumstances exist, e.g. during strong variations of the head or whenutilizing the installation as a turbine and as a pump, it is in practicenecessary for a turbine-generator assembly to be able to be driven attwo different speeds. Alteration of the speed can be effected in anadvantageous manner by altering the electrical pole number of the rotor.

As is known, changeover of the poles of the rotor of a synchronousmachine is effected by reversing the direction of flow of the excitationcurrent in the windings or coils of certain pole groups, whiledisconnecting other pole groups.

In the accompanying drawings:

FIGS. 1 and 2 show electrical circuits with and without poles to bedisconnected, as are known from the state of the art;

FIG. 3 shows an electrical changeover circuit embodying the presentinvention; and

FIG. 4 shows an electrical circuit diagram of the changeover circuitaccording to the invention, with different connection and arrangement ofthe pole to be disconnected.

In order to change over only a single pole, it is necessary to employfour slip rings, as is illustrated by the circuits of FIG. 1.

The slip rings, which are indicated by reference numerals 1, areconnected to reversible pole coils 2, and also to irreversible polecoils 3. Contact brushes 4 act on the slip rings 1 and are connected toan electrical current source indicated diagrammatically by referencenumeral 5. An interrupter and reversing switch 6 is provided which, inpractice, has the purpose of reversing the polarity of the source whichis supplied to the poles and, thereby, of effecting changeover of thepoles.

For the case in which, in addition to reversible poles, disconnectiblepoles are also provided it is for example necessary to employ five sliprings 1, as illustrated in the diagram of FIG. 2. In particular, thefifth slip ring is connected to disconnectible poles 7, which in turnare connected between the irreversible poles and the conductor betweenthe irreversible poles and one of the slip rings 1.

In this case, also, there is provided an interrupter and reversingswitch 6, which has the purpose of reversing the polarity of the currentsupplied for the reversible poles and, simultaneously, excluding theirreversible poles.

As can be seen from the drawings of the prior art arrangements,considerable constructional difficulties arise which can be ascribed tothe large number of slip rings and the associated contact brushes.Furthermore, the fact must be taken into account that in the case offive slip rings, each ring to which no electrical current is provided issubjected to considerable wear. Difficulties therefore arise withrespect to its replacement and its maintenance.

It is accordingly an object of the present invention to avoid theabove-mentioned disadvantages and to provide a circuit for changing thepoles of a rotor of a synchronous machine which enables the possibilitythat reversing and, in some circumstances, disconnecting poles can beeffected using only two slip rings.

It is a further object of the invention to substantially simplify theconstruction of the electrical machine and, for that purpose, to ensurethat the two slip rings employed are always supplied with an electricalcurrent, whereby wear of the rings is substantially reduced.

A further object of the invention is to provide a reversing circuitwhich, in particular, is widely usable and offers the possibility ofaffecting a large number of constructionally different poles, whereby afurther simplification of the machine construction is possible.

An additional object of the present invention is to provide a circuitfor changing the poles of a rotor of a synchronous machine which offersthe greatest possible accessibility and functional security.

According to the present invention, there is provided a circuit forchanging poles of the rotor of a synchronous machine, comprising firstand second slip rings, contact brushes in operative connection with thefirst and second slip rings, means for reversibly connecting the contactbrushes to an electrical current source, reversible pole coilsoperatively connected to one of the slip rings and connected through afirst diode to a circuit portion which is formed by irreversible polecoils, and by a second diode and a third diode, and which is operativelyconnected with the other of the slip rings, and a circuit branchincluding a fourth diode having a polarity reversed with respect to thepolarities of the first, second and third diodes, one terminal of thefourth diode being connected between the reversible pole coils and thefirst diode and the other terminal of the fourth diode being connectedbetween the irreversible pore coils and the second diode.

The invention will be more readily understood from the followingdescription of embodiments of the circuit according to the invention forchanging the poles of the rotor of a synchronous machine.

With reference to FIG. 3 of the drawings, a circuit embodying theinvention for changing over the poles of a rotor of a synchronousmachine has a rotor circuit which is indicated generally by referencenumeral 10 and which is operatively connected at its opposite ends to afirst slip ring 11 and a second slip ring 12.

Brushes 13 act on the slip rings, which brushes are connected toconnections 14 for the supply of electrical current, with an interrupterand reversing switch 15 connected therebetween. Upon alteration of theswitch position, the polarity of the current being supplied is reversed.

The circuit of the rotor 10 includes the coils of reversible poles 20,these coils being connected in series. The poles 20 are connected by aconductor 21 to the first slip ring 11.

The reversible poles 20 are components of a circuit portion 22 whichincludes a first rotary diode 23.

The circuit portion 22 also includes coils 24 of irreversible poles,which coils are connected in series and are operatively connected in thecircuit portion 22 with a second diode 25 and a third diode 26.

The circuit portion 22 is operatively connected, between the seconddiode 25 and the third diode 26, to the second slip ring 12 by aconductor 27.

A circuit branch 30 is also provided and includes a fourth diode 31which has a polarity opposite from that of the previously-mentioneddiodes.

The circuit branch 30 is connected at one end between the reversiblepoles 20 and the first diode 23, and its other end is connected betweenthe irreversible poles 24 and the third diode 25.

As is schematically illustrated in FIG. 3, disconnectible pole coils 40are provided. These can be connected in different ways to the circuit.

In FIG. 3, the disconnectible pole coils 40 are arranged in the circuitportion 22 between the circuit branch 30 and the diode 25.

In FIG. 4, which shows a similar switching circuit, the disconnectiblepole coils 40 are connected between the third diode 26 and theconnection point of the circuit portion 22 to the electrical connectingconductor 27 of the slip ring 12.

It is possible to provide the disconnectible pole coils in other,different positions in the circuit of the rotor, as indicated by squaresin broken lines which are indicated by reference numerals 41 and which,e.g., can be provided before or after the first diode 23, between thecircuit portion 22 and the connection of the branch circuit 30, andbetween the second diode 25 and the conductor 27.

Likewise, the disconnectible pole coils, as is shown in FIG. 4, can beprovided in the branch 30 both before and after the fourth diode 31 andin the circuit portion 22 between the third diode 26 and the point ofconnection of the first diode 23.

With the above-described circuits, it is possible to effect a reversalof the polarity of the current supplied to the reversible poles, wherebythe electrical characteristics of the diodes are utilized. A reversal ofthe polarity of the supplied current, and a reversal of the reversiblepoles, is obtained with only two slip rings, which produces asubstantial constructional simplification.

It can be added that it is possible to produce a circuit in which thediodes have polarities all of which are reversed with respect to thepolarities shown in the drawings.

Furthermore, the diodes in the circuits illustrated may be replaced bycomponents comprising series connections/parallel connections of diodes,in order to be able to adapt to the different current strengths andvoltages.

The reversal of the polarity of the current supplied can, of course, beeffected by other suitable electrical apparatuses, even when notincluding the provision of the interrupter and reversing switch.

In practical application, it occurs that, with the polarity of thesupplied current illustrated in FIG. 3, this current flows in onedirection through the reversible pole coils 20, through the first diode23 to the circuit portion 22, through the irreversible pole coils 24 andthe pole coils 40 which are in some circumstances to be disconnected,and then through the circuit into the second slip ring 12.

Upon reversal of the polarity of the supplied current, the currentalways flows in the same direction through the pole coils 24 (which arenot reversible) and through the third diode 26, then through the branch30 which is controlled by the fourth diode 31 and has a reversedpolarity with respect to the previously mentioned polarities, and thenin the reverse direction through the reversible pole coils 20, but doesnot flow through the disconnectible pole coils 40 since such currentflow is prevented by the second diode 25.

A similar consideration holds true for the disconnectible pole coilswhich are shown in broken lines and indicated by reference numerals 41.

The manner in which the objects are fulfilled by the invention can beunderstood from the above description. The fact is emphasized, at thispoint, that the position of the rotatable diodes makes possible asubstantial simplification, in a constructional respect, of the currentflow path, with all advantages of a constructional and functional type.

The invention can, however, be constructionally modified without fallingoutside of the scope of protection. Also, individual parts can bereplaced by other equivalent components.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A circuit for changingpoles of the rotor of a synchronous machine, comprising:first and secondslip rings; contact brushes in operative connection with said first andsecond slip rings; means for reversibly connecting said contact brushesto an electrical current source; first pole coils operatively connectedto one of said slip rings; a circuit portion operatively connected withthe other of said slip rings and including second pole coils, and firstand second diodes between said second pole coils and said other sliprings; a third diode between said first pole coils and said circuitportion, said first, second and third diodes all being arranged so as topermit the flow of current through said first and second pole coils in adirection towards said second slip ring; and a circuit branch having oneterminal which is connected between said first pole coils and said thirddiode and another terminal which is connected between said second polecoils and said first diode, said circuit branch including a fourth diodearranged so as to permit the flow of current through said first polecoils in a direction towards said first slip ring but to inhibit theflow of current through said second pole coils in a direction towardssaid first slip ring.
 2. A circuit as claimed in claim 1, wherein saidthird diode is connected to said circuit portion between said secondpole coils and said second diode.
 3. A circuit as claimed in claim 1,wherein said circuit portion is connected with said other slip ringbetween said first and second diodes.
 4. A circuit as claimed in claim1, wherein said circuit portion includes third pole coils between saidfirst diode and said other terminal.
 5. A circuit as claimed in claim 4,wherein said circuit portion is operatively connected with the circuitbranch.
 6. A circuit as claimed in claim 1, wherein third pole coils arearranged before and after said third diode between said circuit portionand said one terminal.